Benq Q7T4 (FP71G)

[EGuevarae]

Re: Benq Q7T4 (FP71G)

okay.. Partial success.. the backlights now turn on (got the 2sc's today) and then the monitor just kind of "pixelates" and fades off..

Am recapping the rest of the board now, but anyone got any ideas on what else could cause it ?

I just had that problem (pixelation) on a 940T. The case is as follows:
I bought two units and after recaping I found out that the 2nd one had the right part of the screen pixelated. I pressed the ribbon cable that connects the LCD panel circuit board to the TFT glass/panel/whatever-the-name-is, and ended up with a corrected image but three/four vertical lines across the screen. They didn't go away. You can see the two screens working, and the lines on the one I mention. The portion of the screen at the right of the lines was pixelated BEFORE I PRESSED the ribbon. You can try this to see if that is your case. Crazy Idea, but it is my only pixelation case so far, and I just wanted to suggest it.

[Notherbast]

Re: Benq Q7T4 (FP71G)

Hmmm, will try, thanks.

[EGuevarae]

Re: Benq Q7T4 (FP71G)

Hmmm, will try, thanks.

Any update on this unit? Now I actually have one of them in my workbench. I recapped, and the Backlight turns on, but after 3~4 mins., it turns off. Then after that, just on-off if I power cycle the unit. I haven't checked the 5707s, but I guess I'll start looking for them ...

[Davi.p]

Re: Benq Q7T4 (FP71G)

I'd like to know by those of you that seem to have to do with many monitors to repair and you often tell that you recapped without success in repair, but why don't get an esr meter instead of recapping blindly? I'm also an owner of a broken FP71G+, it has an open pico fuse on the exit 14v line , do you think is enough to replace it only? Caps and other things seems ok visually, also 2 tr. in the path to the output are good, there
seem no other things apart .litics caps.. (not bulged) thanks..

[EGuevarae]

Re: Benq Q7T4 (FP71G)

I'd like to know by those of you that seem to have to do with many monitors to repair and you often tell that you recapped without success in repair, but why don't get an esr meter instead of recapping blindly? I'm also an owner of a broken FP71G+, it has an open pico fuse on the exit 14v line , do you think is enough to replace it only? Caps and other things seems ok visually, also 2 tr. in the path to the output are good, there
seem no other things apart .litics caps.. (not bulged) thanks..

I don't know others, but I do not "blindly recap". You recap when known bad brands under known conditions tend to go bad, and as a starting point you recap to eliminate that variable from the whole equation, especially when visual indication exists. I don't need an ESR meter to replace a Su'scon, a Lelon or another "good" brand on sight. Also, I have repaired monitors without replacing a single cap, so this is not about replacing blindly any cap on the board. On the other hand, caps and other components (like bridge rectifiers, FETs and Transformers) can go bad (open, short, high ESR, lower capacitance,etc.) without visual indication, so "seeing" all components OK just because they are not bulged (in the case of caps) is like "blindly diagnosing".

[Bobdee]

Re: Benq Q7T4 (FP71G)

I'm also an owner of a broken FP71G+, it has an open pico fuse on the exit 14v line , do you think is enough to replace it only? Caps and other things seems ok visually, also 2 tr. in the path to the output are good, there
seem no other things apart .litics caps.. (not bulged) thanks..

That open fuse usually indicates a faulty transistor on Inverter (C5707) there are four of them to check, Also resolder the four Inverter transformers as they are possibly the cause of failure

[Davi.p]

Re: Benq Q7T4 (FP71G)

Thanks Bobdee, in fact some minutes after writing i saw other threads and even if i don't suspected it i found 2 c5707 in short , the solderings are correct. Bye.
(PS: do you remember wich part is compatible with the 2 tr.? If not i'll start searching here, i had read it one time)

[Bobdee]

Re: Benq Q7T4 (FP71G)

Thanks Bobdee, in fact some minutes after writing i saw other threads and even if i don't suspected it i found 2 c5707 in short , the solderings are correct. Bye.
(PS: do you remember wich part is compatible with the 2 tr.? If not i'll start searching here, i had read it one time)

I have repaired many Benq boards with failed C5707s and never found one that did not have bad solder joints on one or more Inverter Transformers, this is what you are likely to find (not easy to see with naked the eye)
https://www.badcaps.net/forum/attach...chmentid=11030
Best resolder them

The transistors are readily available on Ebay, just search for 2SC5707s, they are considered the most suitable for the requirements

[Davi.p]

Re: Benq Q7T4 (FP71G)

Hi, i know this problem, i have watched very well the solderings, that in the picture is
easy to see also by naked eye, i've done a cold soldering by moving the grey .22 cap
near c5707, i can see it quite well, my view is good, there's no cold sold. in mine, i will not touch them cause i can only worse them, i have read a repair guide on net about this monitor, he say that blown tr. are cause by cold sold. on transf. or bad .22 160v grey cap, near the 2 tr. One question, i'm not expert in elect. , i cannot found same part for C5707, i can use another tr. with Vce max 80v (like c5707) but Ic=10A (instead of 8A) even if package is bigger (To220) but seem the pin step near the same, or i have to follow other specs.. (dissipation, mhz)

[Davi.p]

Re: Benq Q7T4 (FP71G)

if package is bigger (To220) but seem the pin step near the same, or i have to follow other specs.. (dissipation, mhz)

Sorry, "is near the same"... and "dissipation"=heat sinking...

[Davi.p]

Re: Benq Q7T4 (FP71G)

i've asked about substitute components for c5707 'cause i also need others components for other things and my benq also has a blown FQU1106 tran.

[mecklan]

Re: Benq Q7T4 (FP71G)

The MOSFETs have I changed the fuse and also the transistors and .22 caps. The other capacitors I have left alone, since I have no direct way to test it. The converter I have soldered, brazed solder removed and resoldered. With the above measures, I have just assembled the TFT again, and lo and behold, it touches on something. Unfortunately, the joy was short-while. The monitor has displayed a picture of exactly 2 seconds and then switched back to orange light. This can be repeated as often as desired. Switched on and off again, then another 2 seconds and picture because that's all well again. What can still be broken?